Double slit experiment

[moshquerade]

the '90s called, they want their coolbeans back.

 

[silverpig]

So I'll chime in here a little.

The double slit experiment is a very nice quantum experiment because it can showcase the oddities of the quantum world at a macroscopic scale that anyone can see with their own eyes and understand... erm, be confused by.

The first few parts are really easy to understand. Stream of particles going through two slits: diffraction pattern. Okay fine. Stream of particles going through one slit: dot. Big deal.

One particle at a time going through one slit or the other: 2 dots. Okay.

One particle at a time going through both slits at once and interfering with itself: diffraction pattern???

Unfortunately I can't explain it without using math, and even still, you don't gain any further understanding other than the math works and you can use it in other situations.

The best conclusion I have been able to draw from this is that in the quantum world there is no such thing as a particle or a wave as we know them. A particle is a concept we have constructed to describe something we see in the natural macroscopic world. This concept does not apply to the quantum world. Similarly, our idea of what a wave is breaks down when we talk about electrons. Sure, we can estimate the "radius" of a particle, and we can talk about a wavelength of another as it travels, but these are just familiar labels we put on something that exhibits some of the same properties as macroscopic phenomena we are accustomed to.

Imagine going back in time and taking an eskimo, someone who has only ever lived way up north in the ice and permafrost, and bringing them to a place where it rains. They wouldn't know what rain was (maybe I'm being ignorant here of the range of weather experienced in the far north, but just go with it), so they'd have to relate it to something they already knew. It'd be "wet snow". Bring that eskimo to the sahara during a sand storm and they'd call it "hard hot snow" or something... but still they'd call it snow as that is all he'd have to relate it to.

Just like that, we call electrons particles, and photons waves, and then say that they can act like both. In reality they're neither.

Oh and about the spin 1/2 thing... It's not actually spin 1/2. It's spin h(bar)/2. When talking about spin it's always assumed you're operating in units of h(bar)... Oh, and here's something else that will probably blow your mind: We don't actually know if anything is spinning. It's just that the electron has some intrinsic property which acts exactly like how we'd expect angular momentum to work.

 

[ja1484]

Originally posted by: Eeezee

Originally posted by: ja1484
Anyone looking for a good read with a surprising amount of factual information on quantum physics (although the book itself is fiction), should read Michael Crichton's "Timeline".

One of the things I love about his work is how while technically fiction, he makes it so scarily plausible. This is because he always bases his stories on new or emerging technologies or fields, and does research on the actual science before creating his fiction story-line around the subject. He took this to the ultimate extreme in his latest novel Next, where the author's introductory note simply reads:

"This book is fiction, except for the parts that aren't."

Originally posted by: destrekor
and, is quantum mechanics dealing with electrons, or with light? I always thought it was light/photons.

+

Technically, Quanta, which are particles that are, theoretically, smaller than subatomic - in other words, smaller than electrons, protons, quarks, etc.

That's not quite right... quantum mechanics deals with electrons, photons, quarks, protons (which are groups of quarks), etc. It precisely describes the Zeeman effect, the Stark effects, ferromagnetism (ie why iron can be magnetized), etc.

You can derive all of chemistry from quantum mechanics. In fact, that's what a fair number of material science physicists do; they derive chemicals that had previously been undiscovered by applying the variational principle (which is a good way to approximate the wave function of particle or group of particles) and basically letting a computer tell them possibly molecular compositions.

I'm sure you're quite right. I'm working with a fuzzy recollection of a layman's terms explanation that was given to me several years back. I'm not in physics to any degree.

 

[RESmonkey]

Wave particle duality. I love physics

 

[spidey07]

Originally posted by: silverpig
Oh and about the spin 1/2 thing... It's not actually spin 1/2. It's spin h(bar)/2. When talking about spin it's always assumed you're operating in units of h(bar)... Oh, and here's something else that will probably blow your mind: We don't actually know if anything is spinning. It's just that the electron has some intrinsic property which acts exactly like how we'd expect angular momentum to work.

That's the rub. And that is what is so confusing to me at least. The equations support it but it is difficult to comprehend as our minds are pre-conditioned to newtonian physics by what we see around us. There is so much that we just don't understand and can't explain.

We still have a lot to learn and I honestly believe we don't really truly understand the forces or what is really going on. It sure is a good trip though.

 

[silverpig]

Originally posted by: Eeezee
NO, that movie is mostly bullshit. They get more than a few things wrong, and a lot of it is trying to relate psychology to quantum mechanics. It was, in fact, funded by some sort of weird religious group.

Dear god I hated that movie. I didn't even finish watching it. They had people who knew nothing about physics talking about it like it was some kind of new age philosophy and... well it was just bad.

 

[halik]

Originally posted by: BrunoPuntzJones

Originally posted by: Analog
The whole point of the observer making the quantum effect choose a state may be a bit off kilter. Basically, the way I interpret it is that we cannot know both the position and momentum of a particle (electron et al), at the same time. The reason is, that we are at the physical limit of detection of such particles. I.e. its like using a baseball bat to figure out how many baseballs are in a canvas sack - the bat is going to "mess up" the baseballs because it interacts with what it is you want to measure. Ideally, you'd want to measure with something that has essentially no interaction with what you're measuring - i.e. a radar device to measure a car's speed. But we have no such device at these geometries, and therefore, the measurement can never reveal both position and momentum. So observation 'messes up' the measurement. Where's Silverpig when you need him!

Not the analogy I would have used, but the latter part is good

Heisenberg was pulled over by a cop.

The cop says, "Sir, do you know how fast you are going?"

To which Heisenberg replies, "No, but I know where I am!"


Announcer: "And horse number 3 wins in a quantum finish!"
Professor Farnsworth: "No fair! You changed the outcome by measuring it!"

I loved that reference; I'm always the only one laughing...

 

[lyssword]

welcome to the internet

 

[Born2bwire]

Originally posted by: spidey07

Originally posted by: destrekor

Originally posted by: DLeRium
As a materials scientist, I don't know how many times we've had go to through diffraction and constructive/destructive interference. It's been too many, but umm... I don't know how mind blowing this is to everyone, but it's a fundamental to my x-rays class and it's just average to me.

can you explain why? even if I knew about this and expected it to occur, not knowing the fundamental reason why would blow my mind.
So, is it only average to you, because you got tired of your mind spazzing out over the fact that you didn't know why, and is now just programmed to think 'meh' so that it doesn't get all erratic again?
If that's the case, that makes sense. I can't function like that though, my brain is constantly striving to find the reasons for why things are the way they are... but that's because I really like discussing different theories. I like engaging in that kind of thought/conversation.

+

We still don't fully understand wave/particle duality. Quantum does a pretty job. But seriously, how the hell can you have something with a spin of 1/2??? Does not compute.

Would you prefer it if we just said spin 1, 2, 3, etc? It's just a number.

 

[Argo]

Originally posted by: destrekor
holy shit. I knew nothing about quantum physics prior to this, and well still don't, but that's kind of mind blowing. I always heard that you change the result of quantum experiments by measuring it, but how the hell does that happen?

and is this merely by 'observing', or some kind of measurement? Say, are the first results determined by nothing observing it and merely observing the result after the test is finished, by looking at a plate that displays where the electrons hit or did not hit?

and, is quantum mechanics dealing with electrons, or with light? I always thought it was light/photons.

+

It makes sense to me. The only way you can "measure" the electron is through one of the 4 basic forces physics (strong, weak, gravity, electro-magnetic). But all these forces are binary, meaning that when you "measure" the electron whatever force it applies on your measuring device, your measuring device applies on the electron, thus affecting it.

The of the electron as the ball. You can't see it because it doesn't emit any light. So the only way you can measure it is either by catching the ball. But once you caught it, it is no longer travelling in it's trajectory.

 

[Kaolccips]

Originally posted by: spidey07
Kaolccips - a spin of 1/2 means it has to be rotated 720 degrees to get back to the original face.

720 degrees? I thought 1/2 would be like.. 180, since 360 is normally .. well a 360.
Guess it doesn't apply to particles. My bad.

Originally posted by: Jeff7

Originally posted by: ConstipatedVigilante
What the fuck? So then, what's my monitor doing when I'm not looking at it? Eh?!!?!?

Watching you masturbate, of course.

Originally posted by: biggestmuff
That's crazy. That's the first time I've seen that. However, they really need to rename that experiment.

Ok, let's see here......ok, the waves are going through the slits, penetrating them.

How about "the double penetration experiment"? That sounds perfectly benign.



And I think that this video's explanation is the sort of thing from which some people get the idea that our observation of the Universe somehow changes it.
The video says that "observing" the electrons in motion changed their behavior.
The observation itself wasn't what caused the change in behavior, as I understand it, but in fact, it's the conditions required to allow observation which would be the problem. If you want to look at something, you need to shine light on it. In the macro world, that's just fine - shine a light on a wall, and the wall won't change appreciably. But start bombarding an electron with photons, and it's going to go nuts. I think that that is where the change in behavior actually comes from.

Eh.. so they did it in absolute darkness the first time? I'm confused.

NO, that movie is mostly bullshit. They get more than a few things wrong, and a lot of it is trying to relate psychology to quantum mechanics. It was, in fact, funded by some sort of weird religious group.

Hey, no one ever said it was all true lol. If you believe everything you hear then you're a tard anyways. I seen it as more of a scifi type thing than a scientific film. But it is fun to watch when you're high

Originally posted by: moshquerade
the '90s called, they want their coolbeans back.

Don't hate. Sorry I'm not up to date with the cool kids lingo.



Basically what it adds up to, is we still don't know jack shit about jack shit.

 

[Eeezee]

Originally posted by: Kaolccips

Originally posted by: spidey07
Kaolccips - a spin of 1/2 means it has to be rotated 720 degrees to get back to the original face.

720 degrees? I thought 1/2 would be like.. 180, since 360 is normally .. well a 360.
Guess it doesn't apply to particles. My bad.

Originally posted by: Jeff7

Originally posted by: ConstipatedVigilante
What the fuck? So then, what's my monitor doing when I'm not looking at it? Eh?!!?!?

Watching you masturbate, of course.

Originally posted by: biggestmuff
That's crazy. That's the first time I've seen that. However, they really need to rename that experiment.

Ok, let's see here......ok, the waves are going through the slits, penetrating them.

How about "the double penetration experiment"? That sounds perfectly benign.



And I think that this video's explanation is the sort of thing from which some people get the idea that our observation of the Universe somehow changes it.
The video says that "observing" the electrons in motion changed their behavior.
The observation itself wasn't what caused the change in behavior, as I understand it, but in fact, it's the conditions required to allow observation which would be the problem. If you want to look at something, you need to shine light on it. In the macro world, that's just fine - shine a light on a wall, and the wall won't change appreciably. But start bombarding an electron with photons, and it's going to go nuts. I think that that is where the change in behavior actually comes from.

Eh.. so they did it in absolute darkness the first time? I'm confused.

NO, that movie is mostly bullshit. They get more than a few things wrong, and a lot of it is trying to relate psychology to quantum mechanics. It was, in fact, funded by some sort of weird religious group.

Hey, no one ever said it was all true lol. If you believe everything you hear then you're a tard anyways. I seen it as more of a scifi type thing than a scientific film. But it is fun to watch when you're high

Originally posted by: moshquerade
the '90s called, they want their coolbeans back.

Don't hate. Sorry I'm not up to date with the cool kids lingo.



Basically what it adds up to, is we still don't know jack shit about jack shit.

To be scifi it would have to have science (even if it's imaginary science). What that movie had could only be described as bullshit, and worst of all it is passed off as a scientific documentary to those who don't know any better.

 

[silverpig]

Originally posted by: Born2bwire

Originally posted by: spidey07

Originally posted by: destrekor

Originally posted by: DLeRium
As a materials scientist, I don't know how many times we've had go to through diffraction and constructive/destructive interference. It's been too many, but umm... I don't know how mind blowing this is to everyone, but it's a fundamental to my x-rays class and it's just average to me.

can you explain why? even if I knew about this and expected it to occur, not knowing the fundamental reason why would blow my mind.
So, is it only average to you, because you got tired of your mind spazzing out over the fact that you didn't know why, and is now just programmed to think 'meh' so that it doesn't get all erratic again?
If that's the case, that makes sense. I can't function like that though, my brain is constantly striving to find the reasons for why things are the way they are... but that's because I really like discussing different theories. I like engaging in that kind of thought/conversation.

+

We still don't fully understand wave/particle duality. Quantum does a pretty job. But seriously, how the hell can you have something with a spin of 1/2??? Does not compute.

Would you prefer it if we just said spin 1, 2, 3, etc? It's just a number.

It's not just a number... there's a reason why it's 1/2, 3/2, 5/2... for one class of particles and 1,2,3... for another.

 

[Born2bwire]

Originally posted by: silverpig

Originally posted by: Born2bwire

Originally posted by: spidey07

Originally posted by: destrekor

Originally posted by: DLeRium
As a materials scientist, I don't know how many times we've had go to through diffraction and constructive/destructive interference. It's been too many, but umm... I don't know how mind blowing this is to everyone, but it's a fundamental to my x-rays class and it's just average to me.

can you explain why? even if I knew about this and expected it to occur, not knowing the fundamental reason why would blow my mind.
So, is it only average to you, because you got tired of your mind spazzing out over the fact that you didn't know why, and is now just programmed to think 'meh' so that it doesn't get all erratic again?
If that's the case, that makes sense. I can't function like that though, my brain is constantly striving to find the reasons for why things are the way they are... but that's because I really like discussing different theories. I like engaging in that kind of thought/conversation.

+

We still don't fully understand wave/particle duality. Quantum does a pretty job. But seriously, how the hell can you have something with a spin of 1/2??? Does not compute.

Would you prefer it if we just said spin 1, 2, 3, etc? It's just a number.

It's not just a number... there's a reason why it's 1/2, 3/2, 5/2... for one class of particles and 1,2,3... for another.

Well no, I mean it's just a matter of units. I can just reassign hbar so that it's double, spins increment by 1 instead of one-half. I don't understand his problem with the idea of a fractional number, they're just eigenvalues indicating a property of the angular momentum.